题解 | 无限长正整数排列字符串

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        StringBuilder S = new StringBuilder();
        int cnt = 1;
        while(S.length()<n){
            S.append(cnt);
            cnt++;
        }
        System.out.println(S.charAt(n-1));
    }
}